In modern motor vehicles, gasoline filters are usually changed cyclically every 30,000 to 60,000 km or also in the case of disturbances in the fuel supply system. This means that a very frequent fuel filter change takes place in light of the large number of registered motor vehicles. If the motor vehicle is turned off, the fuel in the fuel filter is still exposed to overpressure. This means that fuel escapes into the atmosphere when the fuel line is simply removed from the fuel filter. As a result, enormous amounts of fuel enters the atmosphere as a consequence of the frequent fuel filter change and the sometimes large capacity. To avoid this environmental pollution, a device has been known, with which fuel can be drained from the otherwise closed housing of the fuel filter, without fuel escaping into the atmosphere (German Patent No. DE-PS 43 29 258 C1).
This prior-art device for emptying a container, especially a fuel filter of motor vehicles, has a holding means, which comprises essentially a circular disk-shaped base plate. The base plate can be fastened to the fuel filter by means of a holding strap bent in the shape of a half ring. To tighten the holding strap, which surrounds the fuel filter at least partially in the mounted state, a yoke-shaped tightening lever is provided, which can be hung onto the holding strap via a longitudinally adjustable tightening member, so that the tightening length of the holding strap can be adjusted to different diameters of fuel filters.
A drain pipe provided with external threads is fastened on the side of the base plate located opposite the holding strap. A drain channel, whose opening is surrounded on the container side by a ring seal, via which the drain channel is in sealing contact with the container wall, extends through the drain pipe and through the base plate.
A drain container, which has a drilling tool in the form of a twist drill, can be screwed onto the drain pipe via a corresponding screw thread. The twist drill passes through the drain container to its container bottom located opposite the screw thread and is fastened in a firmly seated manner there. The twist drill extends beyond the drain container in the axial direction toward the container, so that when the drain container is screwed onto the drain channel, the twist drill drills through the wall of the fuel filter, and a drain opening is formed in the wall of the fuel filter. The liquid flowing out of the fuel filter through the drain opening directly enters the drain container via the drain channel, without entering into the atmosphere.
After part of the liquid has run off from the fuel filter, the liquid pressure in the fuel filter is reduced, so that the fuel flows into the drain container only very slowly, and the prior-art drain means and the fuel filter form a system which is hermetically sealed to the outside due to the sealing element provided between the base plate and the fuel filter. The consequence of this is that a vacuum is generated in the fuel filter during the continued flow of liquid from the fuel filter, so that no more liquid enters the drain container after a certain amount has flown out. To make it possible to completely empty the fuel filter, a vent opening must be provided in its wall. A type of wrench is provided to create this vent opening. It is a wrench in the manner of a usual pipe wrench, whose gripping jaws are designed to grip around the fuel filter. One of the gripping jaws is provided with a radially inwardly pointing piercing spike, which can be brought into contact with the fuel filter at its top. When the wrench is squeezed, the piercing spike is pressed into the outer wall of the fuel filter, so that the desired vent opening is formed. The drawback of this manner of creating a vent opening in the wall of the fuel filter is that with the fuel filter installed, it is very difficult or even impossible to use the wrench because of the frequently very crowded space conditions in the area of the fuel filter. Furthermore, the wrench itself is very difficult to handle, because strong actuating forces are necessary to pierce the wall to create the vent opening, especially in the case of fuel filters having steel housings.